A leathery, corky, slightly rough, netlike texture of the skin that can be greenish-brown, yellowish-brown, reddish-brown, tan, or gray.
Russeting occurs naturally in some cultivars of apples. It can also be a result of weather; virus, fungal, or bacterial damage; or certain spray applications. .
Naturally occurring russet can almost completely cover the apple skin or be concentrated in the basin (blossom end) or cavity (stem end) or mostly on the sides. It can be present in just trace amounts in any of these same areas. Sometimes only the dots (lenticels) are russeted. It can have a widely open or closely netted appearance or be present in any form from dots to patches to almost complete coverage of the skin.
Pacific Northwest Plant Disease Management Handbook
University of Minnesota Extension